1. Field of the Invention
The present invention relates to an optical film and a display apparatus. Specifically, the present invention relates to an optical film used in a display apparatus including a polarizer in which retardation (Re) in an in-plane direction and retardation (Rth) in a thickness direction are in a specific range.
2. Description of the Related Art
Recently, a liquid crystal display apparatus (LCD) has been widely used, and has been used in a smart phone, a car navigation, a digital camera, a digital signage, and the like which are used outdoors. In addition, various films have been developed according to development of a liquid crystal display market. In general, a film having comparatively small optical anisotropy has been used as an optical film for an LCD. However, recently, it has been proposed that a polyester film having large optical anisotropy is used by being incorporated in a liquid crystal display apparatus (JP4888853B and JP2012-256014A).
For example, in JP4888853B, a polyester film having retardation (Re) in an in-plane direction of 3,000 nm to 30,000 nm is disclosed. In addition, in JP2012-256014A, a polyester film having retardation (Re) in an in-plane direction of 3,000 nm to 30,000 nm is disclosed in which Re/Rth≥0.2. Furthermore, retardation (Rth) in a thickness direction of these polyester films has a positive value.
In JP4888853B and JP2012-256014A, such a polyester film having large optical anisotropy is used in a display apparatus and the like, and thus even when polarized sunglasses are used, excellent visibility is able to be obtained. In addition, when the polyester film is used as a polarizer protection film, rainbow-like color unevenness (rainbow unevenness) does not occur at the time of being observed from an inclined direction.